Cathode



y 1950 B. P. DE LANY ET AL 2,507,435

CATHODE Original Filed Dec. 15,. 1948 2 Sheets-Sheet 1 May 9, 1950 B. P. DE LANY ET AL- CATHODE m 2727272 mza m w e w m4 Wzw m v ZZZ/2 7;

Original Filed Dec. 15, 1948 Patented May 9, 1950 CATHODE Beatrice Pearson De Lany, Miami Beach, Fla., and Paul L. Copeland, Chicago, Ill.

Continuation of application Serial No. 65,408, De-

cember 15, 1948. This'application February 21 1950, Serial No. 145,34? I 13 Claims. (01. 25o 27.5)

This invention relates toa. cathode for mercury arcs andhas for one object to provide a cold cathode electricalv rectifier. form here shown, it may be described as a mer-v cury pool type, cold cathode.

This application is a continuation of our pending application, Serial No. 65,408, filed December 15, 1948, now abandoned, and entitled Cathode.

It has for one object to provide a cathode of the type indicated in which the discharge is initiated easily and may be maintained simply in troublei'ree operation.

. Another object is to provide in a cold cathode device efiective means for securing arc formation and without the necessity of auxiliary starting devices, althoughsuch devices may be used if desired.

In mercury arc cathode devices in the past, substantial and relatively expensive auxiliary equipment has been required for starting the arc, and in general, mercury pool type cathode tubes have been used only in the case of large installations in which the cost and the bulk are not prohibitive. The cost and the bulk have. however, made such equipment generally prohibitively expensive for small tubes and small devices.

Generally, the cathode of this invention comprises a pool of mercur within a glass tube or envelope, and means are provided in one form or another for limiting the area of the mercury pool which is exposed. This may comprise a constriction in the wall of the tube or other envelope within which are are occurs. By this means, the

cathode pool area exposed to the discharge is lim- In the particular I the surface of the constriction is effective in estab-i lishing and maintaining a cathode spot.

The device generally comprises a tube or en; velope formed of insulating material such as glass, Within this is placed a pool of mercury and constricting means are provided which are effective to limit the cathode pool area exposed to the disited to something less than the total area of the pool. ,With this is combined a film of a metal or semi-conductor in electrical contact with the cathode pool within the constriction and connected to a source of positive potential at some distance above the surface of the cathode pool. This film by controlling the charges on the surface of .the constriction is effective in establishing and maintaining a cathode spot.

-"In another form, the device of this invention comprises a cathode pool of large area which is divided by 'a constriction. This constriction produces an inner area of the pool which is relatively small and an outer area which is relatively large. With this, also, is combined a film of metal or semi-conductor in electrical contact with the cathode pool within the constriction and connected to a source '01 positive potential at some distance above the surface of the cathode pool. This film by controlling the electrical charges on wherein:v Y Figure l is a longitudinal section through a tube charge. By means of this construction, an effective mercur arc is provided which operates satis factorily without auxiliary starting equipment, which accomplishes a rapid initiation of the arc and continued satisfactory arc operation. The source of electronsyin all the forms of the device of this invention is a small luminous spot on the surface of the" mercury pool. This spot covers only a small portion of the area the constriction. i

In general, the constriction, at least on its inner surface, contains a material having suitable electrical conductivity. This may be achieved by making the constriction from an insulator which is coated with a thin metallic film or a semi-conducting coating, or it may be accomplished by forming the entire structure of the constriction from a poor electrical conductor or a weakly semiconducting material. In either case, the conducting member is in electrical contact with the cathode pool and at some distance above this with a source of positive potential. Silicon is one of the known suitable semi-conductors. A silicon carbide, such as those used in composition resistors, is a sufficiently poor conductor of electricity to be suitable for this application. a

Mercury has been spoken of above as a suitable metal for forming the cathode pool. Another suitable metal is cesium, which is a metal liquid stable-that is, it is maintained easily and does not tend to disappear. It might be said that the restriction channels the electric current from the anode to the cathode."

.This invention is illustrated more or less diagrammatically in they accompanying drawings,

embodyin the invention;-

of the pool, within Like parts are indicated by like characters throughout the specification and the drawings.

As shown, the tube or envelope comprises .a member I which may be of glass or other insulating material. It is air-tight and the air is exhausted from it. 2 is an anode. 3'is a pool of mercury or other suitablemetal 'which remains liquid at operatin temperatures and which emits electrons freely. 4 is a constriction which; in the case illustrated, is formed of the same material as the envelope l I t i s outwardly f iar ed, as at 5, and is sealedto the enyelope l, as at {5. It thus comprises a generallytubular member 4 flared outwardly at 5, and this tubular member lmay be inwardly reduced or tapered, as at .1. The ends of the portion l project into the. pool of mercury.

8. is a cathode connection which. extends into the mercury cathode pool 3.. The inner surface of the members 4, 5 and l is coated with a thin metallic or semi-conducting surface .portion 9. This metallic or semi-conducting surface portion lies within the tubular part 4', thetapered por: tion 1 and the outwardly flared portion 5. The

metallic film 9, or semi-conducting surface S,

may extend upwardly beyond the-top oithe flared portion 5, or it need not extend fully to the top of that member. The exact upper limits of the area defined by the coating or film 9 is not critical.

A metallic wire Iii projects upwardly within the envelope l and is sealed through the wall of the tube. This wire may be spiraled or positioned about the upper surface of the member 5 and may extend into the tubular portion 4'. The purpose of this spiraling or other shaping of that part of the wire which is in contact with. the metalfilm or semi-conducting area is..to assure a good electrical contact between the wire and the film. If desired, the wire may merely be connected to the film at one point or it may have the substantial contact which would be achieved by placing it in contact with the film throughout an extended area, as indicated by the spiral arrangement. The invention is, however, not limited to any particular, arrangement of the wire Ill and it need only be joined to the film or semi-conducting surface member sufiiciently to assure an adequate electrical contact. 7

A mercury arc cathode tube of a somewhat similar construction is illustrated in co-pending application, Serial No. 38,656, filed July 14., 1948. The device of the present invention for many purposes comprises an improvement of the device shown in that application. The operation of the device may be improved primarily by the uscof an additional electrical connection to the thin metallic film or semi conducting structure 9.

The structure of this invention accomplishes the direct initiation of the spot on the cathode pool without the necessity oi establishing'a visual glow as a preliminary step. The initiation of V the arc is accomplishedby controlling the charge the walls of the constriction member A, I, at cthe cathode pools surface, and also on the'walls extending upwardly toward the positive column.

The wire [0, which is" connccted "to theflu'pper edge of the thin metallic'or semi-conducting film resistance of 45,000 ohms.

or area 9, is connected to a source of positive potential. If the device is to be used as a simple rectifier, this wire l0 may be connected to the anode 2 externally of the envelope 1. If the device is to be used as a controlled rectifier, the potential may comprise a starting pulse phased in relation to the variation of potential on the anode.

Experimental work has been carried out with tubes of the present invention operated on D. C. power supplies. A representative tube had a film In this tube, the anode was operated on a 50-volt supply with suitable current limiting resistors. The starting pulse was applied to the film from an independent supply of 200 volts D. C. The are operated from the 50-volt supply with a current of half an ampere.

Anothertube was arranged toprovide a much lower resistance across members 4 and lot the order of 20 ohms. This tube was started and operated froma 50-vo1t D. C. supply. Resistance was added in series with the starting connection until the current was reduced to.500 ma. Under these conditions, the spot. was established, the are transferred to the anode and operated with a total current of approximately one ampere.

In the modified form of Figure 3, the envelope is generally the same as that shown inFigures 1 and 2 and many of the elements are identical, The same reference numerals are used in the description of Figures .1 and 2. The envelope] is thesarne as that shown in Figure l; the anode} and the mercury pool 3 are the same. The oathode wireor connection 13 is the same in the two figures and the metallic wire 10 is the same. I Instead of the constriction formed of the members a, and l, as shown in Figure l, a funnel-like member i l is used. This member is formed. of asemi-conductor or other poor electrical conductor and it might, for example, be formedof silicon, although it need not be formed of that material and the invention is not limited to the use of silicon or to any other semi-conductor. The funnel II is of such size and shape that it fits tightly within the envelope I. Although it need not be sealed to that envelope and normally will not be sealed, it conforms in shape to the cross section of the envelope and it fits tightly enough within it to avoid displacement and. to retain i s place permanently. It projects into the pool 3 of thecathode and it is connected .to the conducting wire H) which passes through the envelope in the same manner shown in Fig, ure 1. The wire l9 may extend one or more times about the circumference of the member Hor it may merely extend alittle way along the surface of that member in any direction. The degree of contact between the wire Ill and the funneblike member H should be sufiicien't to insure satisfactory electrical contact between the tam members and preferably should be a strong mechanical connection. The wire may, if desired, be embedded the member I l.- The lower end Qf-the funnel H where it proiects'intc thecathode pool 3 forms a narrow opening and hence defines within itself a relatively small area. In this connection, the area of the-portion of the cathode pool defined within themember H and defined within the constricted-portion lot memes of semi-conducting material, it is not necessary to apply a film or coating to its surface such as the film or coating 9 which appears in Figure 1.

Figure 4 illustrates the connection between the anode and the metal member for-med exteriorly of the envelope I. The parts shown in Figure 4 are the same as those shown in Figure 3 except for the addition of the wires or conductors and the resistances. In Figure 4 a wire I2 is connected" to the anode 2 and includes a resistance l3. A wire [4 is connected to the conductor Ill and is connected through a resistance !5 to the wire l2. In the modified form of Figure 5 the envelope, the anode and the cathode connection are the same as those shown in preceding figures and the same reference numerals are applied to them. The metal film I6 is mounted directly upon or formed directly upon the lower part of the" envelope I. The wire I! is in part embodied in the glass wall and is in electrical contact with the metal film l6. Extending upwardly from the wire I! is a conductor H! which is substantially the same as the conductor l shown in the other figures. It is connected through a resistance I9: and a wire 20 to the anode 2 or to the anode support. 7

' Although we have shown an operative form of our invention, it will be recognized that many changes in the form, shape and arrangement of parts can be made without departing from the spirit of the invention, and our showing is, there-, fore, to be taken as, in a sense, diagrammatic.

The use and operation of the invention in any of the forms shown is as follows:

A tube with the cathode of the present construction is inserted in a system where it may be useful. Cathodes of the present design are not limited to use in tubes for any specific purpose. They may be used in rectifier tubes, lighting tubes or any other tubes in which it is desired to use a cold cathode which will start readily without auxiliary mechanism external to the tube and with low current at relatively low potentials.

With the tube embodying the present cathode installed in any such system, the anode 2 and the; cathode pool 3 are connected to sources of current. The wire I!) is also connected to a source of positive potential. When the potential is sufficiently high, a spot is formed within the uncovered area of the cathode pool-that is to say, the spot is formed on the mercury pool within the area bounded by the constriction l of the tubular member 4. After the spot is formed, almost immediately a regular complete arc is developed. This are is transferred to the anode and continues to operate. The arc remains concentrated within the area formed by the con-- striction I.

We claim:

1. In combination, an airtight envelope substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections from the exterior of said envelope to said anode and said cathode, means for concentrating the electron action of the anode upon a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positoned within said envelope and of less diameter than said envelope, said member being in contact with said pool of m etal and being outwardly enlarged at its end away'from" said metal, the innerface of said constriction carrying a thin metallic film, said film being in contact with said metal pool, and a member in electrical contact with said film and extending away from said film.

2. In combination, an airtight envelope substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode, and an anode positioned within said envelope and spaced constriction carrying 'a semi-conductor, said semi-conductor being in contact with said metal pool, and a member in electrical contact with said semi-conductor and extending away from said semi conductor.

3. In combination, an airtight envelope substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode, and an anode positioned within said envelope and spaced awayfrom said cathode, and electrical connections from the exterior of said envelope to said anode and said cathode, means for concentrating the electron action of the anode upon a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positioned within said envelope and of less diameter than said envelope, said member being in contact with said pool of metal and 'being outwardly enlarged at its end away from said metal and sealed to said envelope, the inner face of said constriction carrying a thin metallic film, said film being in contact with said metal pool, and a member in electrical con-' tact with said film and extending away from said film toward said anode.

4. In combinatiornan airtight envelope substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a'cathode, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections from the exterior of said envelope to said anode and, said cathode, means for concentrating the electron action of the anode upon 'a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positioned within said envelope and of less diameter than said envelope, said member being in contact with said pool of metal and being outwardly enlarged at its end away from said metal, the inner face of said constriction carrying a thin metallic film, said film being in contact with said 'metal pool, anda; member in electrical contact with said film and extending away from said film, said conductor being joined to said anode externally of said envelope. 7

5.' In combination, an'airtight envelope formed of insulating material and substantially free from air, a" pool of'metal which is in liquid form at room temperature in said envelope, 'saidxpoolcomprise ing a cathode,.. and an anode positioned-within said-envelope and spaced away from said cathode, and electrical connections from the exterior of said envelope to said anode and said cathode, means for concentrating the electron action of the anode upon a limited portion of the cathode area, said means comprising a constriction placed inthe path of electrons from said cathode to said anode, said constriction comprising a member positioned within said envelope and of less diameter; than said envelope, said member being in contact with said pool of metal and being outwardly enlarged at its end away from said metal andsealedto said envelope, the inner face of said constriction carrying a thin metallic film, said film being in contact with said metal pool, and a member in electrical contact with said film and extending away from said film toward said anode.

- 6.- In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections from the-exterior of said envelope to said anode and said cathode, means for concentratingthe electron action of the anode upon a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positioned withinsaid envelope and of less diameter than said envelope, said member being in contact with said pool of metal and being outwardly enlarged at its end away from said metal and sealed to said envelope, the inner face ofsaid constriction carrying a thin metallic film, said film being in contact with said metal pool, anda metal member in electrical contact with said film and extending away from said film to a temperature in said envelope, said pool comprising a cathode, and an anode positionedwithin said envelope and spaced away from said cathode, and electrical connections from the exterior of said envelope to said anode and said cathode,

means for concentrating the electron action of the anode upon a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positioned within said envelope and of less diameter than said envelope, said member being. in contact with said pool of metal and being outwardly enlarged at its end away from said metal and sealed to said envelope, the inner face of said constriction carrying a thin metallic film, said film being in contact with said metal pool, and a metal member in electrical contact with said film and extending away from said film toward said anode, said conductor being joined to said anode externally of said envelope.

:8. In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode, and an anode positioned within said envelope and spaced away from said cathode, and electr ical connections from the exterior of saidenvelope tos id anode and said cathode, means for concentrating the-electron action of theanode upon a limited-portion of the cathode 8 area, said means comprising a constriction. placed in the path of electrons from said cathode to said anode, said constriction comprising a member positioned within said envelope and of less diam: eter than said envelope, said member being in contact with said pool of metal and being; out wardly enlarged at its end away from said metal and sealed to said envelope, the inner face of said constriction carrying a semi-conductor, said semi-conductor being in contact with said metal p001, and a metal member in electrical contact with said semi-conductor and extending .away from said semi-conductor toward said anode, said conductor being joined to said anode externally of said envelope. v

9. In combination, an airtight envelope formed of insulating material and substantially free from air and an anode positioned within said envelope, a pool of metal, which is in liquid form at the operating temperature, comprising a cathode, and electrical connections from the exterior of said envelope to said anode and said cathode, means for concentrating the electron action of the anode upon a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positioned within said envelope and having a portion of less diameter than said envelope, said member being in contact with said envelope, the constriction be-Q ing formed of semi-conducting material and ,being in electrical contact with said metal pool and a metal member extending away from said semi-. conductor and extending outwardly of and being sealed through the envelope.

10. In combination. an airtight envelope sub: stantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode, and an anode positioned within said envelope and spaced awai. from said cathode, and electrical COIHIEC! tions from the exterior of said envelope to said anode and. said cathode, means for concentrating the electron action of the anode upon. a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positionedi within said envelope and of less diameter than said envelope, said member being in contact with said pool of metal and being outwardly enlarged at its end away from saidmetal, the inner face-of said constriction carrying a, semi-conductor, said semi-conductor being in contact with said metal pool, and amember in electrical contact with said semi-conductor and extending away from said semi-conductor, said conductor being joined to said anode externally of said envelope.

11. In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode, and an anode positioned within said envelope and spaced away from said. cathode, and electrical, connections from. the exterior of said envelope to said anode and said cathode, means for concentrating the. electron action of the anode upon a limited por: tion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a, member positioned within said envelope and of less diameter than said envelope, said member .beingin contact with said pool of metal and being outwardly enlarged at itsfend away from said metal and sealed to said envelope, the inner face of said constriction carrying a semi-conductor, said semi-conductor being in contact with said metal pool, and a member in electrical contact with said semi-conductor and extending away from said semi-conductor toward said anode.

12. In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections from the exterior of said envelope to said anode and said cathode, means for concentrating the electron action of the anode upon a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positioned within said envelope and of less diameter than said envelope,

'said member being in contact with said pool of metal and being outwardly enlarged at its end away from said metal and sealed to said envelope, the inner face of said constriction carrying a semi-conductor, said semi-conductor being in contact with said metal pool, and a metal memher in electrical contact with said semi-conductor and extending away from said semi-conductor toward said anode, said conductor being joined to said anode externally of said envelope.

13. In combination, an airtight envelope formed oi insulating material and substantially free from air and an anode positioned within said envelope, 9, pool of metal, which is in liquid form at the operating temperature, comprising a cathode, and electrical connections from the exterior of said envelope to said anode and said cathode, means for concentrating the electron action of the anode upon a limited portion of the cathode area, said means comprising a constriction placed in the path of electrons from said cathode to said anode, said constriction comprising a member positioned within said envelope and having a portion of less diameter than said envelope, said member being outwardly enlarged at its end away from said metal and in contact with said envelope, the constriction being formed of semiconducting material and being in electrical contact with said metal pool and a metal member extending away from said semi-conductor and extending outwardly of and being sealed through the envelope.

BEATRICE PEARSON DE LANY. PAUL L. COPELAND.

No references cited. 

